http://github.com/jantman/nagios-scripts
This is a collection of some of the Nagios check scripts I've written over the years, as well as some check scripts that I've modified. To the extent possible (the really old ones excepted), I've done my best to follow the Nagios Plugin Development Guidelines.
Most of the script names should be relatively self-explanatory. They should (hopefully) be well documented.
Unless otherwise noted, these scripts are licensed under the terms of the LICENSE file - GPLv3 plus you must retain copyright, authorship and license notices, and modified versions must be clearly identified.
It's not a term of the license, but I strongly request - maybe even beg - you to submit changes/additions/bug fixes back to me as either pull requests (preferred) or emailed diffs. I don't still use a lot of the software that these scripts monitor, so many of them rely on contributions to stay up-to-date.
If you have questions/concerns/find bugs please open an issue on GitHub to let me know.